Blasting initiator composition



Sept. 6, 1955 G. A. NoDDlN ET AL BLASTING INITIATOR COMPOSITION Filed May 2, 1952 IIIIIII III IIIIlJIl lill] JNVENTORS.l GEORGE ADELBERT NODO/N8 CHARLES PHILIP SPAETH 17.117,2@ Patented Sept. 6, 1955 2,717,204 BLASTING INIrrAroR coivwosrrroN George Adelbert Noddin, Clarksboro, and Charles Philip Spaeth, Woodbury, N. J., assignors to E. ll. du Pont de Nemours & Company, Wilmington, Eel., a corporation of Delaware Application May 2, 1952, Serial No. 285,601

3 Claims. (Cl. 52-2) fired either instantaneously with the application of the electric current, or after a predetermined time interval. lt is customary in many cases to include delay compositions in the various caps and to connect the caps located in a number of blast holes in such manner that the caps will tire not instantaneously but successively after prel' determined time intervals. This staggering of shots ensures more efficient blasting results and reduces the vibration effects.

While delay electric blasting caps have been used With advantage for many years, the charges have been of compositions and amounts such that the time intervals between successive shots were generally not less than one-half second. Such delay periods were satisfactory where the only requirement was the firing of the different blast holes in the desired sequence. When it was irnportant, however, to control the timing sufficiently exactly that the desired order of ring Was obtained, with predetermined delay intervals of a tenth of a second or less, the prior art devices have not been satisfactory.

An object of the present invention is a novel burning charge of unusual properties. A further object is a composition possessing ready ignitibility such as to adapt it for use as an ignition charge in electric blasting caps. A still further object is a deflagrating composition adapted to burn without substantial gas evolution. ject is such a composition adapted for use in delay charges in delay electric blasting caps where a very rapid but controlled rate of combustion is required. Additional objects will be disclosed as the invention is described in greater detail in the following.

We have found that the foregoing objects are accomplished when we prepare a burning composition comprising amorphous boron as fuel and red lead (Pb3O4) as oxidizing agent. A desirable composition comprises a mixture of amorphous boron and red lead in the respective ranges of O.5-3.0% and 99.5-97.0%. lf desired, the red lead or the mixture of red lead with boron may be treated with a small amount of a graining or corning agent. This may be accomplished, for example, by adding to the dry red lead or to the intimate mixture of red lead and boron a graining agent or binder comprising a solution of an adhesive material in a suitable solvent, thoroughly blending the materials, and drying the red lead or the mixture thereof with boron at a temperature high enough to remove the solvent. The amount of graining agent thereby A further obdeposited desirably amounts to no more than about 1.5% by weight of the total composition of boron and red lead. Various graining agents are known to the art, such as solutions of gums and shellac. Other graining agents are aqueous solutions of higher polyethylene glycols, water solutions of methyl cellulose, polyvinyl alcohol and the like. We have found that particularly suitable graining agents are benzene solutions of liquid polyfunctional mercaptans such as Thiokol LP2 and aqueous solutions of water-soluble waxes such as compounds and the Carbowaxes,

The invention will be more clearly understood by reference to the accompanying drawings and following examples, which are intended for purposes of illustration only and are not to be taken as limiting in any way.

Figures l, 2, and 3 show the position of a composition in accordance with the foregoing as a delay composition in delay electric blasting caps of different types. Figures 4 and 5 show blasting caps containing a composition in accordance with the invention compressed as the delay charge, and, as the ignition charge, a loose, uncompressed charge of a composition in accordance with the invention.

In Figure 1, for example, 1 designates a substantially cylindrical shell of a copper alloy, having at its base a pressed charge 2 of tetryl. The primer charge 3 of lead azide or other primary detonating compound is shown as embedded in a cavity in the base charge, though it may equally well be present as a pressed superposed charge. The delay composition 8 is present as a pressed charge above the primer charge. The upper end of the shell is closed by the rubber plug 4 through which pass the insulated leg wires 5, which extend below the lower surface of the plug and are connected by the resistant, small-diameter bridge wire 6, about which is positioned the adherent bead of combustible material 7, adapted to become ignited on passage of electric current through the bridge wire. When ignition takes place, the resulting ame tires the delay composition 8.

In Figure 2 a similar delay cap is illustrated, the difference lying in the fact that the delay charge is located within the inverted metal capsule 9, said capsule having a top perforation at 10.

Figure 3 shows another design of delay electric blasting cap, employing the same delay charge. The difference comes in the location of the delay charge 8 within the central bore of the metal carrier 11.

ln Figure 4, shell 1 contains a pressed charge of tetryl 2 and primer charge 3, the primer charge in this case being covered by an inverted metal capsule 9, said capsule having a top perforation 1t). Shell 1 is closed by a rubber plug 4 through which pass leg wires S connected by bridge wire 6. In this figure, the delay composition is present as a pressed charge above the primer charge and its covering capsule. However, above the delay composition is also a capsule 12 having a bottom perforation 13, and within this capsule, surrounding the bridge wire 6 is a charge of a loose ignition mixture 14. When current passes through bridge wire 6, the ignition mixture becomes ignited. When this takes place, the resulting flame lires the delay composition 8. y

Figure 5 shows another design of delay electric blasting cap employing the same delay charge and ignition charge as those of Figure 4, but the delay charge is placed within the central bore of the metal carrier 11 directly above the primer charge without the interposition of a metal capsule.

ExampleY l A fast-burning composition, having the properties of ready ignitibility and controllable rate of combustion,

comprising substantially an intimate blend of amorphous boron and red lead in the proportion of 1 to 99 by weight, respectively, was prepared. The red lead was first grained by adding thereto a 12% aqueous solution of a higher polyethylene glycol, blending thoroughly, and drying to drive off the solvent. The above solution was used in the amount of about 8V cc. per 100 g. of red lead, and the dried product had a content of about 0.72% of the polyglycol. A mixture of the grained red lead and amorphous boron was then made.

The above mixture was used in' a delay electric blasting cap of the type shown inl Figure 1. The following average burning times were obtainedl with different weights of delay mixture, as a result of tests with 10 caps for each weight of charge.

From the foregoing results, it will be seen that fastburning compositions were used, of relatively uniform burning speed for given weights of charge.

Examplel 2 A fast-burning composition was prepared from amorphous boron and red lead in the proportion of 1 to 99 parts by weight, respectively, wherein the red lead was first grained by adding thereto a 10% benzene solution of liquid polyfunctional mercaptans such as Thiokol LP-Z, blending thoroughly, and drying to drive off the solvent. The above solution was used in the amount of 10 cc. per 100 g. of red lead, and the dried product had a content of about 1.0% of the ThiokoL The above mixture was compressed as a delay charge in a delay electric blasting cap of the type shown in Figure 4 at a pressure of 6000 lb./sq. in. An ignition mixture was prepared by mixing intimately 2 parts of amorphous boron and 98 parts of red lead. The mixture was grained by adding thereto a 10% benzenel solution of a liquid polyfunctional mercaptan for instance Thiokol LP-Z, blending thoroughly, and drying tol drive: offthesolvent. The above solution was used in the amount of 1-0 cc. per l-'0`0- g. of the mixture, and the dried product had a content of alittle over 1.0% of the Thiokolf tion mixture was introduced loose and uncompressed in the amount of 4.5 grains above the delay charge. The following average burning times were obtained with different weights of delay mixture, as a result of tests with l0 caps for each weight of delay charge.

Average Burning Time, Milliseconds Over-All Variation, Milliseconds Weight of Delay Charge, Grains Example 3 The igni- .1:

water suspensions of colloidal silica and liquid latex Geon polymers; as well as butyl acetate solutions of nitrocellulose.

Although the mixtures of the present invention would function satisfactorily without a graining agent, it is greatly preferred to use such an agent in order to be able to load the detonators satisfactorily with commercial equipment. Of the various graining agents, those are preferred which permit the material to be consolidated into a plastic mass when pressure is applied, as in the use of the mixtures as delay compositions. Graining agents suitable for this purpose are the liquid polyfunctional mercaptans such as Thiokol LP-2 and the water-soluble waxes, such as the Cal'bov/axes. Amounts of graining agents not less than 0.5% by Weight of the composition and not more than 1.5% are considered satisfactory.

Amorphous boron possesses excellent and unexpected advantages as a fuel for use in burning charges in delay electric blasting caps in that only minute amounts of it are required for the mixture to burn completely and with great uniformity. Although it might be expected that small amounts would be sufficient because of the low molecular weight, the low density, and the fibrous nature of the amorphous boron, it would ordinarily be considered that very small quantities of a fuel in a burning mixture would be detrimental because the fuel would not be adequately distributed to assure continuous burning of the mixture. It is surprising, therefore that the amounts which we have found advantageous, i. e. 0.5 to 3.0% in mixture with 99.5-97% red lead, which amounts are even less than the stoichiometric amounts for complete reduction of the red lead to metallic lead in accordance with the following equation permit a mixture to be obtained in which the fuel and oxidant are sutiiciently well mixed to produce a continuous-burning composition. The use of these small amounts affords mixtures which are not only operative but also are safe to handle and which, when used as delay composition, provide readily controllable delay times. With such mixtures, there is an exceptional degree of uniformity in the delay periods with definite compositions. This latter advantage is important where very short-period delays are needed without danger of overlapping of time intervals. Mixtures containing the amount of boron required to oxidize the red lead completely to metallic lead or larger amounts are not desirable for use in delay electric blasting caps because they are hazardous to handle, being sensitive to impact and friction, and burn with such speed and vigor that, as delay compositions, they would provide insignificant dela and with such evolution of heat that, as ignition compositions, they would be likely to burny through the shell of the blasting cap before the cap could perform its desired function.

In addition, amorphous boron is in itself a material which is` safe to handle, as inthe preparationl of the compositions and the loading of the blasting caps, because it is neither pyrophoric not sensitive to static. Mixtures of boron withred leadin the small proportions which we have found. advantageous are also easy to handle from the point of view of safety, not only because they are adequately insensitive to impact and friction, but also because they do not ignite spontaneously and because they are relatively insensitive to static charges.

Boron compositions have the further advantage of a surprisingly high degree of stability under damp and hot storage conditions. Other advantages comprise the relatively low heat of reaction with oxidants and the low tiring currents required for the ignition of its mixtures.

The uniformity of burning of mixtures of boron with red'lead when they are used as compressed delay charges has been. illustrated inthe examples. Loose mixtures of boron andI red lead also burn with great uniformity.

For example, a mixture containing 1% boron and 99% red lead burns smoothly and regularly, and a mixture containing as little as 0.5% boron will continue to burn. Because of the ability of boron mixtures to maintain their burning, considerable variations can be made within the limits of 0.5-3.0% to yield compositions which will propagate the oxidation reaction. Hence, boron is versatile in its capacity for being variously combined to give compositions having different burning speeds, without the necessity of introducing moderating agents into the composition.

Red lead is the preferred oxidizing agent in mixture with boron as a fuel because it is more readily ignited and more uniform and less hot in its reaction than other inorganic oxidizing agents. Red lead has the further advantage that mixtures containing it can be varied over a wide range of delay times because of the various ways in which the oxide can react, i. e. to yield products of various stages of reduction, as shown by the following equations:

A particular and unusual advantage of boron/red lead mixtures is the fact that they can be used for both the ignition charge and the delay charge in delay electric blasting caps. As ignition compositions, the boron/red lead mixtures are especially advantageous because of their uniformity of burning. They are preferable, indeed, to ignition by means of a bead, the performance of which may be sufficiently erratic in the longer delay periods, e. g. in the range of 500 to 1000 milliseconds, to cause excessive overlap in the intervals of fast delay electric blasting caps. The use of boron/red lead mixtures tngether in delay electric blasting caps as both the ignition charge and the delay charge, as illustrated in Examples 2 and 3, is convenient because preparation and loading are facilitated and because the mixtures, being comprised of the same ingredients, are, naturally, compatible. Furthermore, because mixtures having a wide range of properties for either purpose may be made, the functioning of the delay electric blasting caps can be controlled to a higher degree than heretofore, both with respect to uniformity of ignition and uniformity of delay time. When boron/red lead mixtures are used as ignition compositions, it is desirable that the mixtures contain at least 1.5% and preferably 2% of boron, in order that they may be ignited by the bridge Wire with certainty.

As has been shown, mixtures of boron in small quantities with red lead yield burning charges for use as delay and ignition compositions in delay electric blasting caps which are of an excellence heertofore unknown. The charges are uniform in performance, they can be controlled within narrow limits, they give off little or no gas on burning, they are safe to load and to use, and they are easy to prepare.

The invention has been described at length in the foregoing. It will be understood, however, that many variations may be introduced in details of compositions and arrangements, without departure from the scope of the invention.

We intend to be limited, therefore, only by the following claims.

We claim:

1.' A burning charge for use in delay electric blasting caps which comprises amorphous boron and red lead in the respective proportions of 0.5-3.0% and 99.5-97.0%.

2. A burning charge for use in delay electric blasting caps which comprises an intimate mixture of 0.5-3.0% of amorphous boron and 97.0-99.5% of red lead and includes 0.5-1.5% of a graining agent.

3. An ignition charge for use in delay electric blasting caps which comprises an intimate mixture of l.5-3.0% of amorphous boron and 97-98.5% of red lead and includes 0.5-1.5 of a graining agent.

References Cited in the file of this patent UNITED STATES PATENTS 1,805,214 Hale May 12, 1931 2,309,978 Pratt Feb. 2, 1943 2,410,801 Audrieth NOV. l2, 1946 2,416,639 Pearsall Feb. 25, 1947 2,478,501 Patterson Aug. 9, 1949 2,513,391 Zenftman July 4, 1950 2,587,694 Chalmers et al. Mar. 4, 1952 

1. A BURNING CHARGE FOR USE IN DELAY ELECTRIC BLASTING CAPS WHICH COMPRISES AMORPHOUS BORON AND RED LEAD IN THE RESPECTIVE PROPORTIONS OF 0.5-3.0% AND 99.5-97.0%. 